Permutations of a certain length of a list (combinations, choose k of n, unordered)

ListPermutation.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class ListPermutation {

    public static void main(String[] args) {

        for (int i = 0; i < 6; i++) {
            System.out.println("Take " + i + " of 5: " + permutations(Arrays.asList(1, 2, 3, 4, 5), i));
        }
        System.out.println("Take 1 of 1: " + permutations(Collections.singletonList(1), 1));
        System.out.println("Take 1 of 0: " + permutations(new ArrayList<Integer>(), 1));

    }

    public static <T> List<List<T>> permutations(List<T> input, int select) {

        List<List<T>> res = new ArrayList<>();
        switch (select) {
            case 0:
                break;
            case 1:
                for (T t : input) {
                    res.add(Collections.singletonList(t));
                }
                break;
            default:
                for (int i = 0; i < input.size(); i++) {
                    T current = input.get(i);
                    List<T> subListBeforeCurrent = input.subList(0, i);

                    for (List<T> permutation : permutations(subListBeforeCurrent, select - 1)) {
                        List<T> currentRes = new ArrayList<>();
                        currentRes.addAll(permutation);
                        currentRes.add(current);
                        res.add(currentRes);
                    }
                }
        }
        return res;
    }
}

@doubleday your comment on the Java solution wouldn't work because Collections.singletonList(t) (from case 1) doesn't allow .add() ;)

but my solution was also not correct in case 0, which should return an empty list inside the "result" list (selecting 0 out of n has always one solution, the empty list - otherwise it doesn't match https://en.wikipedia.org/wiki/Pascal's_triangle)

v2 fixes that, and actually doesn't need case 1 anymore, so of course we can simplify the loop (and yes start at 1 makes more sense..)
https://gist.github.com/LuzianW/4937cc6a5c98b1e07a6f

Excellent Code Luz!!